The present invention generally relates to a system for coupling bone portions across a fracture and, more specifically, to an intramedullary nail or plate and screw assembly used to treat fractures of long bones, such as the femur, humerus, and tibia, fractures of the intertrochanteric region, and various periarticular fractures of these and other bones.
There are a variety of devices used to treat fractures of the femur, humerus, tibia, and other long bones. For example, fractures of the femoral neck, head, and intertrochanteric region have been successfully treated with a variety of compression screw assemblies, which include generally a compression plate having a barrel member, a lag screw and a compressing screw. In such systems, the compression plate is secured to the exterior of the femur, and the barrel member is inserted in a predrilled hole in the direction of the femoral head. The lag screw has a threaded end, or another mechanism for engaging bone, and a smooth portion. The lag screw is inserted through the barrel member so that it extends across the break and into the femoral head. The threaded portion engages the femoral head. The compression screw connects the lag screw to the plate. By adjusting the tension of the compression screw, the compression (reduction) of the fracture can be varied. The smooth portion of the lag screw is free to slide through the barrel member to permit the adjustment of the compression screw. Some assemblies of the prior art use multiple screws to prevent rotation of the lag screw relative to the compression plate and barrel member and also to prevent rotation of the femoral head on the lag screw.
Compression plates may be of the locking or non-locking variety. Generally, non-locking bone plates have a plurality of non-threaded holes for receiving non-locking screws. Non-locking screws are screws that are not secured to a plate. Non-locking plates depend on friction between the screw and bone for stability. Therefore, non-locking plates have a low resistance to shear force which can cause screw loosening, but non-locking plates have the advantage of allowing the screw to compress the bone across a fracture site.
In contrast, a locking plate has threads on an inner surface of the screw holes that correspond to threads on an outer surface of a head of the locking screw. Locking plates and screws have a fixed relationship that the stability at the screw and plate hole does not rely on screw purchase in bone. As such, locking screws have a high resistance to shear force, which can reduce bone vascular damage and result in better clinical results, but locking plates have a disadvantage in that the screw head engages the threaded hole on the locking plate before the screw can compress the plate to bone and/or the bone across the fracture site.
Intramedullary nails in combination with lag screws or other screw assemblies also have been successfully used to treat fractures of the femur, humerus, tibia, and other long bones as well. A significant application of such devices has been the treatment of femoral fractures. A typical prior art intramedullary nail may have one or more transverse apertures through its distal end to allow distal bone screws or pins to be screwed or otherwise inserted through the femur at the distal end of the intramedullary nail. This is called “locking” and secures the distal end of the intramedullary nail to the femur. In addition, a typical intramedullary nail may have one or more apertures through its proximal end to allow a lag screw assembly to be screwed or otherwise inserted through the proximal end of the intramedullary nail and into the femur. The lag screw is positioned across the break in the femur and an end portion of the lag screw engages the femoral head. An intramedullary nail can also be used to treat shaft fractures of the femur or other long bones.